The present invention relates to a positioning device for a brake mechanism and in particular to such a device which can securely fasten a brake block to a brake arm by means of spherical surfaces between the means so as to be adjustable in any desired direction.
In the past, brake blocks made of rigid rubber served to stop bicycle wheels and were integral with a bolt in order to be fixed on a brake arm by a nut, so that the brake block was in a constant direction of contact with the rim of a bicycle wheel. However, the brake block will be deformed after a long period so as to vary the relative angle between the brake block and the rim. Such a condition reduces braking efficiency. So, those skilled in this art improved the brake mechanism by inserting a packing ring and a washer between the brake block and brake arm and between the brake arm and nut respectively. In this conventional braking mechanism, shown in FIG. 1, a packing ring 91 and a washer 92 are respectively provided on each side of the brake arm 6. The area of central bores of the packing ring 91 and washer 92 is larger than the cross-section of the bolt 81. Therefore, the brake block can rotate through a slight angle by means of the gap between the packing ring 91, washer 92 and bolt 81, and the spherical contacting-surface between the packing-ring 91 and nut 7. However, some disadvantages still exist, for example, it is necessary to dismount the nut 7 before setting the desired position of the brake block 8 and then to adjust the packing ring 91 and washer 92, and lastly mount the nut 7. But the packing ring 91 and washer 92 are still shiftable during the mounting operation, in other words, the operative procedure is complicated and inaccurate.